308-OR: The Circadian Clock Exerts Coordinated Control of Beige Adipocyte Development via Cytoskeleton-MRTF/SRF Signaling Cascade

The circadian clock confers temporal regulation in metabolism, and its disruption leads to obesity and insulin resistance. In the current study, we identify that the opposing circadian clock regulators, transcription activator Bmal1 and its repressor Rev-erbα, exert concerted control of the actin cytoskeleton-MRTF/SRF pathway to drive beige adipocyte development, and that this clock regulatory axis is required for beige fat thermogenic capacity. Key components of the MRTF/SRF signaling display circadian oscillations in beige fat, and cistromic analyses revealed Bmal1 and Rev-erbα chromatin occupancy of genes involved in MRTF/SRF regulation. Genetic loss- or gain-of-functions of Bmal1 and Rev-erbα in adipogenic precursors markedly altered actin cytoskeleton organization. Bmal1 silencing inhibits F-actin formation and MRTF/SRF activity whereas its forced expression augments actin cytoskeleton. Notably, Bmal1 and Rev-erbα transcriptional control of the MRTF/SRF signaling modulates beige fat thermogenic capacity in vivo. Prrx1-Cre-mediated subcutaneous beige fat-selective Bmal1 ablation induced browning with augmented mitochondrial metabolism, resulting in resistance to obesity that improved insulin sensitivity. Conversely, overexpression of Bmal1 in beige depot suppressed the thermogenic program with adipose expansion and impaired glucose tolerance. In contrast, Rev-erbα gain-of-function phenocopied that of Bmal1 ablation, leading to browning of beige fat, resistance to obesity and insulin sensitivity. Mechanistically, we show that genetic loss of Bmal1 enhanced beige precursor differentiation and thermogenic induction, whereas Rev-erbα overexpression similarly promoted beige adipogenesis. Collectively, these findings uncover a novel concerted circadian clock control in beige adipocyte development that determines thermogenic capacity via the cytoskeleton-MRTF/SRF signaling cascade. Disclosure X.Xiong: None. W.Li: None. R.Liu: None. V.Yechoor: n/a. K.Ma: None. Funding NIH 1R01DK112794 to KM and DK097160 to VY